THERMO-PNEUMATIC AND PIEZOELECTRIC ACTUATION IN MEMS-BASED MICROPUMPS FOR

THERMO-PNEUMATIC AND PIEZOELECTRIC ACTUATION IN MEMS-BASED MICROPUMPS FOR BIOMEDICAL APPLICATIONS ME 381 – Final Project Kenneth D’Aquila and Sean Tseng Northwestern University 12/10/07

Outline Motivation Thermo-Pneumatic Actuation Piezoelectric Actuation Comparison Summary

Motivation Drug Delivery Systems (DDS) Implantable Transdermal Staples M; Daniel K; Cima M; Langer R. Pharmaceutical Research 2006, 23, 847 -863 Micro Total Analysis System (µ-TAS) “lab on a chip” Zhang C; Xing D; Li Y. Biotechnology Advances 2007, 25, 483– 514

Thermo-Pneumatic Micropumps Basic Mechanism 1. 2. 3. Resistive heating Air expansion Membrane deflection Inlet Valve Typical Voltage: 1 -20 V Typical Pump Freq: 1 -2 Hz ε = δV/ V 0 = compression ratio Outlet Valve “Dead Volume” (V 0) Stroke Volume (δV) Pumping Chamber Actuation Chamber Flexible Membrane Resistive Heater Trapped Fluid

Analytical Models Improving Efficiency by Modeling 1. Resistive heating 2. Air expansion 3. ΔH = CpΔT Pwr=U 2/R ΔH=∫(Pwr)dt Ideal Gas Law Membrane deflection Spherical Geometry Plate Theory T = temperature d = duty ratio τ = pump period R = resistance Cp = heat capacity U = voltage ΔH = enthalpy P = Pressure V = air volume L = chamber radius h = membrane deflection m= membrane thickness v =poisson’s ratio

Response to Input Variables Optimizing Electrical Energy Input (Qualitatively) Mor e Flex ible Jeong O; Yang S. Sensors and Actuators 83. 2000 249– 255 Nozzle/Diffusers Val ve -Les s Flow. Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123– 124. 2005 453– 458 Yoo, J; Choi Y; Kanga, C; Kim Y. Sensors and Actuators A 139 2007 216– 220.

Choosing Pump Type Selecting Appropriate Flow Rate (Qualitatively) PERISTALTIC-TYPE: 21. 6 µL/min BUBBLE-TYPE: 0. 023 µL/min . Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123– 124. 2005 453– 458 Jun D; Sim W; Yang S. Sensors and Actuators A 139 2007 210– 212

Microfabrication Cost-Effective Fabrication/Materials ed Sili s -Ba n co Jeong O; Yang S. Sensors and Actuators 83. 2000 249– 255 ed s -Ba S PDM . Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123– 124. 2005 453– 458

Brief History on Piezoelectricity “Piezo” is Greek word for pressure “Piezo effect” discovered in 1880 by Curie bros. “Inverse piezoelectric effect” proved using thermodynamics by Lippmann Difficult mathematics resulted in very few advancements until World War I, when it was used in sonar to detect submarines Much research from WWII and on from USA, Japan and USSR Led to lead zirconate titanate (PZT), most used piezoelectric ceramic today

Piezoelectric Fundamentals PZT unit cell above TCurie (left) and below TCurie (right) Unit cell on the right deformed tetragonally allowing for piezoelectric effect http: //www. physikinstrumente. com

Tensor Mathematics http: //www. physikinstrumente. com

Tensor Mathematics (Cont’d) http: //www. physikinstrumente. com

Piezoelectric Actuation Benefits Unlimited theoretical resolution Limited by noise from electric field, mechanical design, mounting flaws, etc. Sub-nano resolutions still achievable No moving parts No frictional wear from sliding or rotating parts

Actuation Mechanism (Cantilever Valve) Koch, M. , Harris, N. , Evans, A. G. R. , White, N. M. , Brunnschweiler, A. , “A novel micromachined pump based on thick-film piezoelectric actuation, ” Solid State Sensors and Actuators, 1997. TRANSDUCERS '97 Chicago. , 1997 International Conference on Volume 1, 16 -19 June 1997 Page(s): 353 - 356 vol. 1 Diaphragm pump using cantilever valves. Results in fatigue and variable flow rate over time.

Microfabrication (Cantilever Valve) Made from three silicon wafers (Layers #1 and 2 are identical) Etched anisotropically using KOH Cantilevers made by B+ anisotropic etch stop Layer #3 made with time-controlled KOH anisotropic etch with LPCVD silicon nitride mask Wafers are anodically bonded together Gold cermet printed on, dried and heated PZT layer printed on, 3 MV/m electric field applied for polarization Final gold cermet printed on PZT, dried and heated

Actuation Mechanism (Valveless) Cui, Q. F. , Liu, C. L. and Zha, X. F. , “Study on a piezoelectric micropump for the controlled drug delivery system, ” Microfluid Nanofluid 3 2007 377– 390 Valveless diaphragm pump. No moving parts resulting in higher reliability and more consistent flow rate over time.

Microfabrication (Valveless) Deep Reactive Ion Etching (DRIE) or precision turning for cylindrical volume Pump membrane usually from outside supplier Piezoelectric transducers from supplier but can be cut to shape with excimer laser machining Transducers bonded to membrane with conductive epoxy glue Diffuser/nozzle are laser micromachined Inlet/outlet are etched anisotropically with KOH

Governing Equations Pressure loss coefficient given by:

Governing Equations (Cont’d) Cui, Q. F. , Liu, C. L. and Zha, X. F. , “Study on a piezoelectric micropump for the controlled drug delivery system, ” Microfluid Nanofluid 3 2007 377– 390

Governing Equations (Cont’d) The diffuser efficiency is given by: If the pressure loss coefficient in the nozzle is greater, then η>1 and there is net flow from the inlet

Governing Equations (Cont’d) The transverse deflection of the pump membrane is given by: Difficult to solve due to non-steady state flow and coupling effects between transducer/membrane, membrane/fluid

Numerical Solution Eq. 8 is difficult to solve analytically so a numerical solution must be found Use Finite Element Analysis and software ANSYS Mu, Y. H. , Hung, Y. P. , and Ngoi, K. A. , “Optimisation Design of a Piezoelectric Micropump, ” Int J Adv Manuf Technol 15 1999 573 -576

Input Variables Input factors include the following: Membrane material Membrane thickness Piezoelectric thickness Input voltage Response is maximum membrane deflection Area under deflection is stroke volume Analogous to flow rate

Maximum Deflection vs Input Mu, Y. H. , Hung, Y. P. , and Ngoi, K. A. , “Optimisation Design of a Piezoelectric Micropump, ” Int J Adv Manuf Technol 15 1999 573 -576

Quantitative Comparison Name Year Variant Type Nozzle/Diffuser, Corrugated Membrane Input Electrical 8 V, 40% Duty at 4 Hz Flow Rate Materials Jeong 2000 14 µL/min Doped Silicon Jeong 2005 Peristaltic, Flat Membrane 20 V, 50 % Duty at 2 Hz 21. 6 µL/min PDMS, Cr/Au Jun 2007 Surface Tension, Air Bubble 3. 5 V 0. 023 µL/min, 116 n. L in 5 min PDMS, Ti/Al Van de Pol 1990 Check Valves, Flat Membrane ? ? ? V, 0. 5 Hz 30 µL/min, Silicon Yoo 2006 Nozzle/Diffuser, Flat Membrane 500 m. W, 1% Duty at 2 Hz 0. 73 µL/min PDMS, ITO Yoo 2007 Nozzle/Diffuser, Flat Membrane 500 m. W, 7% Duty at 2 Hz 1. 05 µL/min PDMS, ITO, Parafilm Cui 2007 Nozzle/Diffuser, Piezoelectric Diaphragm 60 – 140 V Koch 1997 Cantilever Valve, Piezoelectric Diaphragm 100 – 600 V 10 – 120 µL/min Silicon Wan 2001 Nozzle/Diffuser, Piezoelectric Diaphragm 3 V 900 µL/min Silicon 10 – 100 µL/min Silicon

Qualitative Comparison Piezoelectric actuation No frictional wear Very high resolution Lots of work already completed and can predict performance (ANSYS simulations) Thermo-Pneumatic Large stroke volume but low frequency Simple design and easy fabrication Warms fluid

Conclusion Choosing one type of actuation over another depends strictly on application Thermo-Pneumatic has lower flow rate allowing for more precise dosage If reliability is more important and high voltage is allowed, then piezoelectric actuation is better Simulations using FEA and ANSYS can help determine performance and appropriateness for application